refactor: convert Path object to string for file saving in _save_every_k_gens function

Author: soto-raul

libensemble/manager.py

@@ -348,7 +348,7 @@ def _save_every_k_sims(self, complete: bool) -> None:
     def _save_every_k_gens(self, complete: bool) -> None:
         """Saves history every kth gen step"""
         self._save_every_k(
-            Path(self.libE_specs["workflow_dir_path"]) / "{}_{}after_gen_{}.npy",
+            str(Path(self.libE_specs["workflow_dir_path"]) / "{}_{}after_gen_{}.npy"),
             self.hist.index,
             self.libE_specs["save_every_k_gens"],
             complete,